我试着找到答案，但没有看到一个针对我的特定问题。我正在使用三元搜索树的共享指针（用于预测文本算法），并使用共享指针遇到一些问题。
我已经离开C ++ 5年了，让我告诉你，Java并没有帮助你学习指针。在过去的几天里，我不得不重新学习我在5 - 6年前在学校学到的指针素材，并成功地破坏了我的代码。
以下是我的大部分代码：
// TernarySearchTree.cc
#include "stdafx.h"
#include "ternary_search_tree.h"
//Constructor
TernarySearchTree::TernarySearchTree() {
num_nodes_ = 0;
size_in_memory_ = 0;
root_node_ = nullptr;
}
TernarySearchTree::TernarySearchTree(const TernarySearchTree& other) {
num_nodes_ = other.num_nodes_;
size_in_memory_ = other.size_in_memory_;
TernarySearchTreeNode node;
node = *other.root_node_;
root_node_.reset(&node);
}
//Destructor
TernarySearchTree::~TernarySearchTree() {
}
//operators
TernarySearchTree& TernarySearchTree::operator=(const TernarySearchTree& other) {
//TODO: swap idiom - create a copy of the node then swap the new one with it
//do this first to provide exception safety
TernarySearchTreeNode node;
node = *other.root_node_;
root_node_.reset(&node);
num_nodes_ = other.num_nodes_;
size_in_memory_ = other.size_in_memory_;
return *this;
}
//Convert from string to c-style string
std::vector<char> TernarySearchTree::ConvertStringToCString(std::string str) {
std::vector<char> wordCharacters (str.begin(), str.end());
//remove newlines or tabs
if (wordCharacters.back() == '\n' || wordCharacters.back() == '\t') {
wordCharacters.pop_back();
}
wordCharacters.push_back('\0');
return wordCharacters;
}
//Insert a node
TernarySearchTreeNode TernarySearchTree::InsertNode(TernarySearchTreeNode ¤tNode,
char character,
NodePosition position,
bool isRoot) {
TernarySearchTreeNode newNode;
newNode.set_character(character);
if (!isRoot) {
switch (position) {
case NODE_POS_LEFT:
currentNode.set_left_node(newNode);
break;
case NODE_POS_CENTRE:
currentNode.set_centre_node(newNode);
break;
case NODE_POS_RIGHT:
currentNode.set_right_node(newNode);
break;
default:
break;
}
}
return newNode;
}
//Insert a word
void TernarySearchTree::InsertWord(std::string word) {
std::vector<char> characters = ConvertStringToCString(word);
std::shared_ptr<TernarySearchTreeNode> currentNode = 0;
bool isFirstCharacter = true;
//Add each character to a node while traversing
//Base case where there is no root node
if (!root_node_) {
for(std::vector<char>::iterator it = characters.begin(); it != characters.end(); ++it) {
if (*it != '\0') {
//if it is the first character
//root_node_ is equal to the address of new node
if (isFirstCharacter) {
std::cout << "HIHI";
TernarySearchTreeNode node = InsertNode(*currentNode, *it, NODE_POS_CENTRE, true);
root_node_.reset(&node);
currentNode.reset(&node);
isFirstCharacter = false;
} else {
TernarySearchTreeNode node = InsertNode(*currentNode, *it, NODE_POS_CENTRE, false);
std::cout << std::endl << node.get_character();
currentNode.reset(&node);
}
}
}
//If not base case, then we need to compare each character
} else {
currentNode = root_node_;
for(std::vector<char>::iterator it = characters.begin(); it != characters.end(); ++it) {
if (*it != '\0') {
currentNode.reset(&SetNextNode(*currentNode, *it, *std::next(it, 1)));
} else {
currentNode->set_end_of_word(true);
}
}
}
}
//Recursive function for obtaining/adding the next node when inserting a word
TernarySearchTreeNode TernarySearchTree::SetNextNode(TernarySearchTreeNode ¤tNode, const char currentChar, const char nextChar) {
//If characters match
if (currentChar == currentNode.get_character()) {
//if centre node exists
if (currentNode.get_centre_node()) {
return *(currentNode.get_centre_node());
//Otherwise, create a new node and recall method on that node
} else {
//If not the end of the word, make a new node with the next letter
if (nextChar != '\0') {
return InsertNode(currentNode, nextChar, NODE_POS_CENTRE, false);
} else {
return currentNode;
}
}
//If it is less, follow node on the left
} else if (currentChar < currentNode.get_character()) {
//if left node exists, recursive call
if (currentNode.get_left_node()) {
return SetNextNode(*(currentNode.get_left_node()), currentChar, nextChar);
//Otherwise, create a new node and recall method on that node
} else {
return SetNextNode(InsertNode(currentNode, currentChar, NODE_POS_LEFT, false), currentChar, nextChar);
}
//Otherwise it is bigger, so take right path
} else {
//if right node exists, recursive call
if (currentNode.get_right_node()) {
return SetNextNode(*(currentNode.get_right_node()), currentChar, nextChar);
//Otherwise, create a new node and recall method on that node
} else {
return SetNextNode(InsertNode(currentNode, currentChar, NODE_POS_RIGHT, false), currentChar, nextChar);
}
}
}
//Populate the TST from a word list/file
void TernarySearchTree::PopulateTreeFromTextFile(std::string fileName) {
std::ifstream file;
std::string line;
file.open(fileName);
if (file.is_open()) {
//Assume text file has one word per line
while (std::getline(file, line)) {
InsertWord(line);
}
}
}
//Search
bool TernarySearchTree::SearchForWord(std::string word) {
return false;
}
int _tmain(int argc, _TCHAR* argv[])
{
//Test
TernarySearchTree tst;
//Open file
tst.PopulateTreeFromTextFile("simple.txt");
//start at root and follow some paths
std::cout << tst.get_root_node();
/**std::vector<char> vec;
vec.push_back('a');
vec.push_back('c');
std::vector<char>::iterator it = vec.begin();
std::cout << *std::next(vec.begin(), 1);
std::cout << (*it < 'c');
it++;
std::cout << *std::next(it, 0);
std::cout << (*it < 'c');
**/
return 0;
}
和节点：
/*TST node methods */
#include <iostream>
#include "ternary_search_tree_node.h"
/** ADD COPY CONSTRUCTOR*/
//Constructors
TernarySearchTreeNode::TernarySearchTreeNode() {
character_ = '\0';
end_of_word_ = false;
left_node_ = nullptr;
centre_node_ = nullptr;
right_node_ = nullptr;
}
TernarySearchTreeNode::TernarySearchTreeNode(const TernarySearchTreeNode& other) {
character_ = other.character_;
end_of_word_ = other.end_of_word_;
TernarySearchTreeNode leftNode;
leftNode = *other.left_node_;
left_node_.reset(&leftNode);
TernarySearchTreeNode centreNode;
centreNode = *other.centre_node_;
centre_node_.reset(¢reNode);
TernarySearchTreeNode rightNode;
rightNode = *other.right_node_;
right_node_.reset(&rightNode);
}
TernarySearchTreeNode::TernarySearchTreeNode(char character, bool end_of_word,
TernarySearchTreeNode left_node,
TernarySearchTreeNode centre_node,
TernarySearchTreeNode right_node) {
character_ = character;
end_of_word_ = end_of_word;
left_node_.reset(&left_node);
centre_node_.reset(¢re_node);
right_node_.reset(&right_node);
}
//Destructor
TernarySearchTreeNode::~TernarySearchTreeNode() {
left_node_.reset();
centre_node_.reset();
right_node_.reset();
}
//operators
TernarySearchTreeNode& TernarySearchTreeNode::operator=(const TernarySearchTreeNode& other) {
if (&other) {
TernarySearchTreeNode leftNode;
leftNode = *other.left_node_;
TernarySearchTreeNode centreNode;
centreNode = *other.centre_node_;
TernarySearchTreeNode rightNode;
rightNode = *other.right_node_;
left_node_.reset(&leftNode);
centre_node_.reset(¢reNode);
right_node_.reset(&rightNode);
character_ = other.character_;
end_of_word_ = other.end_of_word_;
}
return *this;
}
//printing
std::ostream& operator<<(std::ostream& os, const TernarySearchTreeNode& obj)
{
// write obj to stream
char c = obj.get_character();
bool b = obj.is_end_of_word();
os << c << "\t is end of word: " << b;
return os;
}
当我在调试模式（Visual Studios）中运行时，它能够设置根节点，但是当它输入第二个节点时，它会崩溃尝试删除＆＃34; stuff＆＃34;当currentNode在函数 InsertWord 的else语句中调用.reset（＆amp; node）时。我在复制构造函数或operator =方法或析构函数中做错了吗？它上方的cout行确实打印了正确的字母，因此看起来节点正在正确创建。
调试调用堆栈显示：
TernarySearchTree.exe！std :: _ Ref_count_base :: _ Decref（）第118行C ++ TernarySearchTree.exe！的std :: _ Ptr_base :: _ Decref（） 第347行C ++ TernarySearchTree.exe！的std :: shared_ptr的:: shared_ptr的〜（） 第624行C ++ TernarySearchTree.exe！的std :: shared_ptr的::复位（） 第649行C ++ TernarySearchTree.exe！TernarySearchTreeNode ::〜TernarySearchTreeNode（） 第50行C ++ TernarySearchTree.exe！TernarySearchTreeNode ::`标量 删除析构函数＆＃39;（unsigned int）C ++ TernarySearchTree.exe！的std :: _ Ref_count :: _ destroy（）方法 第161行C ++ TernarySearchTree.exe！std :: _ Ref_count_base :: _ Decref（） 第120行C ++ TernarySearchTree.exe！的std :: _ Ptr_base :: _ Decref（） 第347行C ++ TernarySearchTree.exe！的std :: shared_ptr的:: shared_ptr的〜（） 第624行C ++ TernarySearchTree.exe！的std :: shared_ptr的::复位（） 第649行C ++ TernarySearchTree.exe！TernarySearchTreeNode ::〜TernarySearchTreeNode（） 第50行C ++
TernarySearchTree.exe！TernarySearchTree :: InsertWord（性病:: basic_string的，标准::分配器 第105行C ++ TernarySearchTree.exe！TernarySearchTree :: PopulateTreeFromTextFile（std :: basic_string，std :: allocator） fileName）第182行C ++ TernarySearchTree.exe！wmain（int argc，wchar_t * * argv）第200行C ++ TernarySearchTree.exe！__ tmainCRTStartup（）第533行 TernarySearchTree.exe！wmainCRTStartup（）第377 C行 kernel32.dll！7592338a（）未知[下面的框架可能不正确 和/或缺失，没有为kernel32.dll加载符号]
ntdll.dll！77599f72（）未知ntdll.dll！77599f45（）未知
感谢您提供的任何帮助！如果还有其他需要我提供的内容（我正在阅读的文本文件中只有corn），请告诉我。
答案 0 :(得分：5)
您的问题是您在C ++中使用Java风格。与Java中的所有内容本质上都是指针不同，在C ++中，您必须考虑值，引用，指针和对象生存期之间的差异。
这个功能不好：
TernarySearchTreeNode::TernarySearchTreeNode(char character, bool end_of_word,
TernarySearchTreeNode left_node,
TernarySearchTreeNode centre_node,
TernarySearchTreeNode right_node) {
character_ = character;
end_of_word_ = end_of_word;
left_node_.reset(&left_node);
centre_node_.reset(¢re_node);
right_node_.reset(&right_node);
}
您正在通过值获取TernarySearchTreeNode个对象，然后将其地址放入shared_ptr。 shared_ptr获取动态分配对象（使用new创建的对象）的所有权，并在引用计数变为零时删除它。上面的对象（left_node等）是堆栈对象，它们将在函数末尾超出范围。当您将地址放入shared_ptr时，它会稍后尝试删除这些对象，但它们不再存在。
就推荐如何解决这个问题而言，这里有很多假设刚刚结束。例如，子节点可以有多个父节点吗？复制节点真的有意义吗？
我现在假设复制节点有意义，因此使用shared_ptr是合理的。在这种情况下，我们可以从这里开始：
TernarySearchTreeNode TernarySearchTree::InsertNode(std::shared_ptr<TernarySearchTreeNode currentNode>,
char character,
NodePosition position,
bool isRoot) {
auto newNode = std::make_shared<TernarySearchTreeNode>();
newNode->set_character(character);
if (!isRoot) {
switch (position) {
case NODE_POS_LEFT:
currentNode->set_left_node(newNode);
然后，set_left_node等所有功能也应将std::shared_ptr<TernarySearchNode>作为参数。您不应该调用reset()，它允许shared_ptr获取空闲指针的所有权（refcount == 1）。 shared_ptr通过在析构函数中增加复制和解除引用的引用计数来工作。当您取消引用指针然后获取地址时，您正在使用shared_ptr。